Based on physical model of high power laser amplifier, simulation software used to analyze laser fluence distribution and performance of amplifier was developed. The object-oriented design method is applied in the software and different laser amplifier can be simulated. By comparison with the simulated results by the other simulation softwares and experimental results of SG-ⅠⅠ laser amplifer, it can be showed that this software can simulate different laser amplifier flexibly and truly.